text: Acid Base Accounting (ABA), namely, the practice of quantifying sources of acidity and alkalinity, is a critical aspect of managing acid sulfate soils. For example, ABA is used to calculate the amount of neutralising agent (e.g., lime) required to neutralise stockpiled sulfidic material generated from excavation or dredging activities.  
  The standard Australian ABA system describes three operationally defined pools of acidity (mol H per tonne dry soil).  
  Potential Sulfidic Acidity (PSA) is a measure of the ‘oxidisable sulfur’ associated with Reduced Inorganic Sulfur (RIS) (e.g., iron sulfides and elemental sulfur) that may oxidise to produce sulfuric acid.  
  Titratable Actual Acidity (TAA) is a measure of soluble and exchangeable acidity associated with organic acids and loosely bound Al and Fe ions – which react with water to produce H (i.e., hydrolysis).  
  Retained Acidity (RA) is a measure of sparingly soluble sulfates such as [https://www.mindat.org/min-2078.html jarosite] and [https://www.mindat.org/min-7281.html schwertmannite], which slowly generate acidity via the release and hydrolysis of Al and Fe.  
  The Acid Neutralising Capacity (ANC) of the soil sample is subtracted from the sum of the PSA, TAA and RA to calculate the net acidity. ANC is typically associated with carbonates and, to a lesser extent, organic matter.  
  In Australia, net acidity is used in combination with the texture or clay content of the sample and the weight of acid sulfate soil to be disturbed (e.g., excavated for construction) to determine whether or not an Acid Sulfate Soil Management Plan (ASSMP) is required as part of statutory environmental management protocols.